Pacemaker leads form the electrical connection between a cardiac pacemaker pulse generator and the heart tissue that is to be stimulated. As is well known, the leads connecting such pacemakers with the heart may be used for pacing or for sensing electrical signals produced by the heart or for both pacing and sensing in which case a single lead serves as a bidirectional pulse transmission link between the pacemaker and the heart. The lead typically comprises a distal end portion carrying a tip electrode and a ring electrode. The lead may also carry one or more cardioverting and/or defibrillating electrodes proximal of the ring electrode.
Various lead types for different placement approaches have been developed. Thus, an endocardial type lead is one that is inserted into a vein and guided therethrough into a cavity of the heart. The distal end of an endocardial lead may carry a helical, screw-in tip element, electrically active or inactive, and/or outwardly projecting tines or nubs for anchoring the lead.
Epicardial or myocardial type leads are attached directly to the epicardium using sutures or another fixation mechanism such as a helical screw-in electrode that engages the myocardium. Myocardial leads typically are used for temporary pacing or for permanent pacing following open-heart surgery. Conventional approaches to the placement of current myocardial leads usually involve thoracotomies. Such placement techniques have disadvantages including the relatively large incisions needed to gain access to the thoracic cavity and to the heart; the difficulty of quickly and easily attaching the lead; the high rate of patient morbidity, trauma and pain; the tendency to require longer in-patient recovery times; and the unattractiveness of the scars left by the procedure.
To mitigate these disadvantages, minimally invasive lead placement systems have been developed for placing a screw-in myocardial lead on the surface of the heart via a small, finger size opening in the chest. Such systems may include a fiberoptics video camera of the type commonly used in other thoracic surgeries (for example, lung biopsies and other thoracic cavity and cardiac procedures) for visually imaging, and thereby aiding, the lead placement procedure. These minimally invasive lead placement systems allow for faster, safer and easier myocardial lead placements with significantly less morbidity, trauma and pain to the patient.
Another example of a minimally invasive lead placement system is found in U.S. Pat. No. 5,052,407. That patent discloses a lead including an electrically active distal region having a preformed, planar, spiral configuration. Using a stylet or guide wire, the distal region of the lead is maneuvered into the pericardial sac of the heart through a small needle puncture in the sac's outer membrane or layer. Once the distal region of the lead is inside the pericardial sac, the stylet or guide wire used to place the lead is withdrawn. As the stylet or guide wire is retracted, the turns of the spiral form in succession within the sac. The relatively large diameter spiral tends to keep the distal region from backing out of the sac without the spiral straightening out, lending a certain degree of stability to the lead. Nevertheless, still further improvement in the anchoring of such lead types would be desirable.